1. Field of the Invention
The present invention relates to an apparatus for rotating a magnetic disc, for example a flexible disc which is contained within a protective casing or cassette of plastics material. The disc is of the type which has a central hole and an entrainment opening, which may be a slot.
The apparatus comprises a hub member provided with a flat surface on which the magnetic disc can be supported, and mounted on a shaft which is rotatable with respect to a fixed carrier. The shaft projects with respect to the flat surface of the hub member and can pass with play through the central hole in the disc. An entrainment peg is mounted on the hub member and projects from the flat surface thereof for the purposes of coupling to the entrainment opening in the disc.
2. Description of the Prior Art
An arrangement is known in which the entrainment peg is supported from oppositely disposed sides by two arms of a flexible plate in such a way as to permit the peg to tilt in a radial direction. In this arrangement, the entrainment peg is disposed at a predetermined and fixed distance D1 from the axis of rotation of the hub member. The distance D1 is less than the distance D2 between an outside edge of the entrainment opening and a reference edge of the central hole in the disc, so that, when the shaft fits through the central hole in the disc and the entrainment peg is coupled to the entrainment opening, the peg is forced into the opening and, by being tilted displaces the disc radially with respect to the shaft, positioning it with respect to the latter.
In the known arrangement however the entrainment peg is free also to tilt in a direction perpendicular to the radial direction, the plate member which carries it also being yielding in that direction.
That disadvantage causes incorrect angular positioning of the magnetic disc with respect to the shaft and since in the equipment which deals with this type of discs, the angular reference is normally made at the shaft, the above-indicated angular positioning error consequently gives rise to inaccurate positioning of the recording and reading heads in relation to the magnetised tracks on the disc.